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What role does sulfur play in vulcanizing natural rubber?

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In the process of vulcanization, sulfur acts as a chemical agent that transforms raw, sticky rubber into a durable, elastic solid.12

When heated with rubber, sulfur reacts with the polymer molecules to form covalent cross-links, or bridges, between adjacent long-chain molecules. These sulfur interlinks (–S $_{n}$ –) create a permanent molecular network that prevents the molecules from flowing past one another, which allows the material to maintain its shape and elasticity even at high temperatures.12

Additionally, the introduction of sulfur disrupts the regularity of the rubber molecules, which impedes crystallization and prevents the material from becoming hard and brittle at low temperatures. By chemically tying the molecules together, sulfur effectively converts a viscous liquid into a resilient, solvent-resistant elastomer.21